I use FCP 5.1, i know it's pretty old, but it usually works fine.
I captured my DV tape, and all the settings are in DV. Now when I modify the video, or add text to it, there's no problem on the canvas. Only the quality of the video and text in the viewer drops. As I export it QT without convention, the QT video is very low quality. Like in the viewer... Even! If I only add text you'll see that the exported video looks fine until the text comes in, than it's total chaos, and the it looks fine again after the text has gone..
I'd love a new version of FCP, but I think not just becouse of an old version of FCP
The canvas shows the modifications and texts just fine..